This invention relates generally to medical implants, and more particularly to apparatus for applying tension along or across a ligament to repair, augment, or replace it, or applying tension across a bone fracture to reduce it.
Medical implants for tensioning purposes typically comprise one or more tensile members (e.g., sutures or orthopedic cables) connected to one or more anchors (e.g., suture anchors or suture locks) to create a converging tensile force between the two anchors. This general concept has been used in the orthopedic and sports medicine fields to repair torn or damaged tendons and ligaments, to replace missing or displaced tendons and ligaments, and to anchor grafted or artificial tendons and ligaments to bones so that they can grow back together.
Prior art anchor/tensile member configurations typically fall into three functional categories; (1) a configuration in which the tensile member in held in place by an interference fit between the tensile member and bone, (2) a configuration in which the tensile member is tied, glued, melted, or otherwise connected to the anchor during manufacturing or intraoperatively, and (3) a configuration in which the tensile member is tensioned or made tight with the use of one of many available and well-known slip-knots.
It is often desirable to have the ability to tension the configuration provisionally (i.e. without setting a final irreversible tension) so that the effect of a particular level of tension can be evaluated and have the opportunity to “settle in” before it is made permanent.
However, one problem with prior art anchors is that they do not generally permit accurate provisional tensioning. When standard suture anchors are used, the tension is set by estimating the length of the final suture implant or tying a slipknot that can be tightened by hand. Some are even tensioned by wrapping the suture around a Kirschner wire (“K-wire”) and twisting the wire to tighten. Even if the initial tension is estimated well, suture will settle into the soft tissue around it and lose tension after implantation. There does not currently exist a good way to tension a suture to a known load, “trial” its tension and allow for some settle in, re-tension, and repeat as needed.
Another problem with prior art suture tensioning techniques is that of determining that excessive tension is applied. More specifically, because the tension in a suture strand does not exceed its failure load during the operative procedure does not mean it will not experience a load greater than its failure load during cyclic loading in-situ.